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The present invention relates to occupancy sensors.
A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
An occupancy sensor is an energy conservation device designed to detect the presence of human occupant(s) in a given area. When occupancy is sensed, the various electrically-powered loads in that area controlled by the sensor (for example, lights, ventilation, and the like) are energized. When that same area has been unoccupied for a predetermined period of time, the sensor de-energizes the electrical loads that it controls. Occupancy sensors may therefore conserve a great deal of energy in areas where the occupants do not exercise diligence in de-energizing those electrical loads when they leave the area.
Over the last few decades, several events have led to the growth of a large consumer market for energy saving devices including occupancy sensors. First, there has been an increase in public awareness of energy conservation and its beneficial environmental consequences. In addition, there has been increased realization by both private and government-controlled power generation industries of the economic and environmental advantages of energy conservation as a means of meeting peak load power demands. Finally, there have been legislative mandates at the federal, state and local levels for the use of energy conserving devices, such as occupancy sensors, in government and other public buildings.
Occupancy sensors have been successfully designed and tested using a variety of technologies. A brief description of the most widely used occupancy sensor technologies along with the strengths and weaknesses of those technologies follows:
Active Ultrasonic Acoustic Doppler Occupancy Detection
This technology allows continuous detection of moving objects that reflect ultrasonic acoustic energy. This method of occupancy detection is highly sensitive since it is based on an active source of ultrasonic acoustic energy. An apparatus and method of this type are disclosed in U.S. patent application Ser. No. 08/384,580, filed Feb. 6, 1995, assigned to the same assignee as the present invention and entitled: OCCUPANCY SENSOR AND METHOD FOR OPERATING SAME, the disclosure of which is incorporated herein by reference.
However, this method of occupancy detection has several limitations: first, it is insensitive to motion that is orthogonal to the direction toward the receiver; second it is insensitive to motion generally not in the line of sight of the receiver; third, it is subject to false tripping due to other sources of ultrasonic energy; fourth, it is subject to false tripping due to heating and air conditioning air flow; and finally, it has no means of range discrimination. Since occupancy sensors based on Doppler techniques have no means of range discrimination, a large-distant target moving at approximately the same speed as a smaller, nearby target might have similar target signatures.
Active Electromagnetic Doppler Occupancy Detection
This technology allows continuous detection of moving objects that reflect electromagnetic energy. This method of occupancy detection is highly sensitive since it is based on an active source of electromagnetic energy. However, this method of motion detection also has several limitations: first, it is insensitive to motion that is orthogonal to the direction toward the receiver; second, it is insensitive to motion generally not in the line of sight of the receiver; third, it is subject to false tripping due to other sources of electromagnetic energy; and finally, it has no means of range discrimination.
Passive Audio Acoustic Occupancy Detection
This technology allows continuous detection of objects that emit audio acoustic energy. This method of occupancy detection is quite sensitive but is subject to false tripping due to non-occupant sources of audio acoustic energy such as facsimile machine, telephone and security system tones, automobile and emergency vehicle horns, etc.
Passive Infrared Occupancy Detection
This technology allows continuous detection of moving objects that emit infrared energy. This method of occupancy detection is also quite sensitive even though it is based on passive sensing of moving sources of infrared energy. This method of occupancy detection also has several limitations: first, it is insensitive to sources generally not in the line of sight of the receiver; second, it is subject to being blinded by intense, stationary sources of infrared energy; third, it is subject to false tripping due to rapid fluctuations in the intensity of stationary infrared sources; and finally, it is subject to a detection coverage tradeoff involving the number of lens facets versus detection range.
Position Sensor Based Occupancy Detection
This technology uses one or more mercury switches to sense changes in the physical position of the sensor. This technology has several limitations: first, it is insensitive to minor motion that may be indicative of occupancy; and second, it is inherently a digital (off/on) device.
Piezoelectric Sensor Based Occupancy Detection
This technology senses the changes in the resistance of a piezoelectric sensor to sense occupancy. This technology is subject to false tripping due to changes in temperature.
Significant innovation in the design of occupancy sensors has occurred over the last few decades. The early occupancy sensors utilized primarily analog signal processing techniques. The large area motion sensor described in U.S. Pat. No. 3,967,283 by Clark et. al., issued Jun. 29, 1976, utilized electromagnetic motion detection and was based on analog signal processing techniques. The occupancy sensor described in U.S. Pat. No. 4,661,720 by Cameron, Jr. et. al., issued Apr. 28, 1987, and the low voltage motion sensor for activating a high voltage load described in U.S. Pat. No. 4,820,938 by Mix et. al., issued Apr. 11, 1989, utilized analog signal processing techniques. The variable gain amplifier used in these sensors required manual adjustment. The room occupancy sensor, lens and method of lens fabrication described in U.S. Pat. No. 5,221,919 by Hermans, issued Jun. 22, 1993, utilized passive infrared detection and was based on analog signal processing techniques. The motion detection sensor with computer interface described in U.S. Pat. No. 5,281,961 by Elwell, issued Jan. 25, 1994, utilized active ultrasonic motion detection and was based primarily on analog signal processing techniques. Although easy to design and relatively cheap to implement, the analog filters in these devices had filter response characteristics that drifted with temperature variations and that varied over the lifetime of the various analog filter components. The overall result of using a sensor based on analog signal processing techniques was an occupancy sensor whose performance was unpredictable.
Additionally, the majority of these early occupancy sensors were based on a single sensing technology. Since each technology has its own inherent limitations, these sensors were subject to false tripping due to a variety of sources. For example, ultrasonic Doppler sensors were subject to false trips due to air conditioning and heating system air flow. In addition, since these sensors had no means of range discrimination, they were subject to false trips due to motion outside the desired range of interest. Similarly, passive infrared (PIR) sensors were subject to being blinded by intense, stationary sources of infrared energy. The automatic lighting device described in U.S. Pat. No. 4,751,399 by Koehring et. al. issued Jun. 14, 1988 utilized only acoustic motion detection. This sensor was subject to false tripping due to non-occupant sources of audio acoustic energy such as facsimile machine, telephone and security system controller tones, emergency vehicle and automobile horns, etc. The selective illumination technique described in U.S. Pat. No. 4,225,808 by Saraceni issued Sep. 30, 1980 allowed the use of pressure, ultrasonic motion, microwave, photoelectric and audible sound sensors but failed to combine these technologies to achieve a more reliable sensor with a reduced probability of false tripping. In order to lessen the probability of false trips, the user was often forced to reduce the sensor""s sensitivity. The overall result of using a sensor based on a single technology was an occupancy sensor with reduced sensitivity and reliability.
The next generation of occupancy sensors used two or more sensing technologies. These sensors typically required the user to specify a separate activation threshold for each detector technology in the sensor. The digital detector output of each sensor technology was then combined using classical digital logic to detect occupancy. The preset light controller including infrared sensor operable in multiple modes described in U.S. Pat. No. 5,128,654 by Griffin et. al., issued Jul. 7, 1992, used infrared and visible light sensors. The dual technology motion sensor described in U.S. Pat. No. 5,189,393 by Hu, issued Feb. 23, 1993, combined the outputs of its ultrasonic and infrared sensors using classical Boolean AND and OR hardware logic. In general, these multiple sensing technology sensors had better performance than their predecessors but still exhibited a sensitivity-false alarm tradeoff. For example, if the various detector signals were combined using the logical OR function, the overall sensitivity of the sensor increased at the expense of an increased incidence of false trips. On the other hand, if the various detector signals were combined using the logical AND function, the overall incidence of false trips decreased at the expense of decreased sensor sensitivity. Since each sensing technology has its own separate activation threshold, these sensors were often unable to reliably detect motion in marginal cases where one or more sensing technologies observed signal levels just below the user-defined threshold level. The overall result of using these early multiple sensing technology-based occupancy sensors was an improved performance occupancy sensor that was unable to sense occupancy in the more complex marginal sensor signal level situations.
In general, prior art occupancy sensors heretofore known suffer from a number of disadvantages, including:
1. Lack of a sophisticated multiple sensing technology sensor signal conditioning to more completely exploit the advantages of sensing technologies while minimizing disadvantages. The prior art failed to combine the various occupancy sensor detection technologies in a sophisticated fashion to increase the overall probability of occupancy detection while simultaneously lowering the overall probability of false tripping.
2. Lack of adaptive sensor behavior. The prior art failed to produce an occupancy sensor whose performance adapted over time to optimize the sensor""s performance.
3. Lack of digital signal processing techniques. The prior art used analog signal processing techniques. The analog filters used in these sensors required manual tuning that was a costly, time consuming process. In addition, the performance of these analog filters was temperature dependent and drifted with time.
4. Lack of means to simply and efficiently communicate the status of the sensor to installation and maintenance personnel. An occupancy sensor, typically has a number of settings that determine its mode of operation, and that the person who installs or maintains the sensor may wish to review. The sensor is typically installed out of reach on a ceiling or wall such that its adjustment knobs or dials are not readily visible. The prior art does not incorporate a system to make such settings readily available and apparent to a person who wishes to query them.
5. Lack of means to check status of the controlled signal to determine if a load device is connected, or if the controlled output is misconnected or shorted.
6. Lack of permanent storage of sensor variables. The prior art failed to permanently store various sensor settings. In the event of a power failure, these sensors had no means of recovering their previous settings.
7. Lack of no means to recognize an excessively reverberant controlled space with excessive ultrasonic return signal amplitude, and lack of means to compensate by adjusting the ultrasonic transmitter amplitude.
8. Lack of ultrasonic receiver preamplifier and demodulator performance monitoring means. The prior art did not monitor ultrasonic receiver preamplifier and demodulator performance and did not have means for making adjustments to accommodate a poorly executed installation or highly acoustically reflective space. A sophisticated ultrasonic sensor incorporates a high gain receiver preamplifier that may become saturated due to excessive acoustic reflections from room walls and other hard structures within the space. Furthermore, the sensor may be installed incorrectly too close to a fixed acoustic reflector such as a wall, exit sign, or other architectural feature. Saturation of the receiver preamplifier causes the motion signal to be lost, and the sensor to be effectively blinded by the excessive signal level. It is desirable that the sensor may be installed by unskilled personnel, and that the sensor be able to accommodate non-ideal situations created either by improper installation or difficult acoustic environments. The prior art has no means to determine saturation of the receiver preamplifier, nor any means to correct for such saturation.
9. Lack of occupancy cycle detection and utilization. The prior art did not detect the typical daily and weekly occupancy cycle of the sensor""s environment and use that information to make occupancy decisions. A workspace is typically occupied according to a cycle that varies predictably throughout the day, and also according to a set pattern through the work week. Heretofore, sensors have not taken into account this pattern, and the prior art has no means to survey and record the typical daily and weekly occupancy patterns, nor to store that information, nor to act on the basis of that information.
The present invention solves the above-noted failings in the prior art by providing an occupancy based load controller, comprising a plurality of occupancy sensors for producing a respective plurality of occupancy estimator signals, each indicative of motion within a space; a programmable microprocessor, connected to the plurality of occupancy sensors, for calculating a composite occupancy estimator from the plurality of occupancy estimator signals, and for comparing the composite occupancy estimator to a composite activation threshold; and a controllable load energizing device responsive to the programmable microprocessor, operable to automatically energize an electrical load when the microprocessor determines that the composite occupancy estimator is greater than the composite activation threshold. The programmable microprocessor can also operate to compare the composite occupancy estimator to a composite maintenance threshold, and the controllable load energizing device is then operable to continue energizing the electrical load when the microprocessor determines that the composite occupancy estimator is greater than the composite maintenance threshold.
The plurality of occupancy estimator signals are preferably digital representations based on signal levels detected at the plurality of occupancy sensors. The invention contemplates the use of any type of occupancy sensor technology, in any combination, including, for example, an ultrasonic transmitter and sensor, a passive infrared (PIR) detector, a passive audio acoustic detector, and a microwave transmitter and sensor, or any combination of two or more of these sensor technologies.
The composite occupancy estimator may be calculated by any useful mathematical combination of the plurality of individual occupancy estimator signals, for example, arithmetic sum, weighted arithmetic sum, or Yager Union function of the plurality of occupancy estimator signals. In addition, the composite occupancy estimator can be created by performing a table look-up based on the plurality of occupancy estimator signals.
The composite activation and maintenance thresholds can be programmable.
The sensitivity of at least one of the plurality of occupancy sensors may be adjusted in accordance with the present invention, for example based upon an historical usage patterns of the space, based upon detection of false-on events, or based upon detection of false-off events.
The invention may also include an environmental sensor, connected to the microprocessor, for sensing an environmental condition of the space, including, for example, an ambient temperature sensor or an ambient light sensor.
An additional feature of the invention is the storing of a status of the load controller; and visually reporting the status of the load controller. Status may be reported at predetermined time intervals, or upon user interrogation, for example upon detecting a predetermined motion pattern.
When incorporating an ultrasonic transmitter and sensor, the ultrasonic transmitter may operate to transmit continuous wave ultrasonic signals; and the ultrasonic sensor may include an ultrasonic signal receiver, and a controllable gain preamplifier circuit having an input connected to receive a Doppler-shifted ultrasonic signal produced by the ultrasonic receiver, and an output providing a Doppler-shifted ultrasonic signal with controllable amplitude. The ultrasonic sensor further comprising a zero crossing phase lock loop sampling point circuit having an input connected to receive a sampling point control signal; and an output providing a sample of the Doppler-shifted ultrasonic signal near a zero crossing point of the Doppler shifted ultrasonic signal.
The invention also contemplates a method for controlling an electrical load as a function of occupancy of a space, comprising generating a plurality of occupancy estimator signals indicative of motion within a space; calculating a composite occupancy estimator from the plurality of occupancy estimator signals; comparing the composite occupancy estimator to a composite activation threshold; and energizing the electrical load when the composite occupancy estimator is greater than the composite activation threshold. Further, the method may compare the composite occupancy estimator to a composite maintenance threshold; and continue to energize an electrical load when the composite occupancy estimator is greater than the composite maintenance threshold.
The calculating step may be accomplished by any useful mathematical function, including, for example, calculating the composite occupancy estimator by performing an arithmetic sum of the plurality of occupancy estimator signals, by performing a weighted arithmetic sum of the plurality of occupancy estimator signals, or by performing a Yager Union function of the plurality of occupancy estimator signals. The method may also be accomplished by performing a table look-up based on the plurality of occupancy estimator signals.
The method also programmably adjusts the composite activation and composite maintenance thresholds.
The invention also contemplates a method for controlling an electrical load as a function of occupancy of a space, comprising transmitting continuous wave ultrasonic signals into the space; receiving a Doppler-shifted ultrasonic signal reflected from the space; sampling the Doppler shifted ultrasonic signal near a zero crossing point of the Doppler shifted ultrasonic signal to provide a sampled Doppler-shifted ultrasonic signal; detecting occupancy of the space as a function of the sampled Doppler-shifted ultrasonic signal; and energizing the electrical load when the sampled Doppler-shifted ultrasonic signal indicates that the space is occupied. The sampling step may be performed by sampling the Doppler-shifted ultrasonic signal as a function of continuous wave ultrasonic signals transmitted into the space.
The invention also contemplates a method of operating an occupancy based load controller, including: at least one occupancy sensor for producing at least one occupancy estimator signal indicative of motion within a space, a programmable microprocessor, connected to the at least one occupancy sensor, for comparing the occupancy estimator signal to a predetermined threshold; and a controllable load energizing device responsive to the programmable microprocessor, operable to automatically energize an electrical load when the microprocessor determines that the occupancy estimator signal is greater than the predetermined threshold; the method comprising maintaining a status of the occupancy based load controller; detecting a predetermined motion pattern within the space; and reporting the status upon detection of the predetermined motion pattern.
Accordingly, some exemplary features and advantages of embodiments of the present invention include the use of a sophisticated multiple sensing technology based sensor fusion detection algorithm. This algorithm combines the outputs of a plurality of occupancy sensors, including, for example, ultrasonic, PIR, microwave and acoustic sensors, to produce a composite occupancy estimator signal that is compared to a composite threshold to determine occupancy. This produces a highly sensitive yet highly reliable occupancy sensor.
The present invention also contemplates a variety of self-adaptive features. These adaptive features may be individually enabled or disabled by proper setting of the sensor""s user-controlled option switches. In general, the longer the sensor is allowed to adapt within a given environment, the better its occupancy detection performance will be.
The invention also provides a means to simply and efficiently communicate the status of the sensor to installation and maintenance personnel. In accordance with the present invention, a visual indication of the sensor""s internal settings and variables is reported in the form of a sequence of light flashes, encoded to represent the numerical values. It also emits character descriptors of its state of operation, for instance, satisfactory, failed, or otherwise non-optimal, in the form of a sequence of light flashes. Thus it is possible for the sensor to communicate key portions of its internal state information to installers or maintenance personnel. This communication takes place from a distance, without a need to physically access the sensor.
A portion of the sensor""s status information may be emitted automatically at periodic intervals. One embodiment of the present invention is also able to recognize a choreographed sequence of hand movements that instruct the sensor to output a detailed sequence of status descriptors and variable information upon command. Upon receipt of this sequence of movements, the sensor enters an information retrieval mode, and detailed internal state information is emitted in a predetermined sequence. Thus it is possible for installation or maintenance personnel to query the sensor for status and receive a detailed report. Both the query and receipt of the report occur from a distance by using the occupancy sensing function of the sensor, without a need to physically access the sensor and without the need to provide dedicated hardware to shift the sensor from a normal mode of operation to a status reporting mode.
The present invention also may incorporate means to store adapted sensor variables such that they are maintained if power to the sensor is disconnected. It is generally preferred that an occupancy sensor be powered continuously. In numerous applications, however, the power supply to the sensor is connected in series with a wall switch that controls the lighting. This often occurs in retrofit situations where the sensor power supply and relay are connected into existing lighting circuits in the most expedient way, near the lighting fixture, and in the portion of the circuit already switched at the wall. In such situations, the sensor will periodically loose power, and it is essential that it maintain its previously adapted settings.
The present invention also incorporates means to determine if the ultrasonic receiver preamplifier is saturated, and means to adjust the phase of the sample point of the synchronous demodulator circuit relative to the outgoing carrier signal by searching for the zero crossing of the preamplifier signal. This ensures that the synchronous demodulation sample is taken at the optimum point, and that the performance of the receiver is not adversely affected by preamplifier saturation that occurs between the zero crossings of the signal. Furthermore, if due to extreme preamplifier saturation the sample point search algorithm is unable to find a sample point that has sufficient saturation margin, the algorithm then decreases the transmitter drive amplitude in order to reduce the excessive signal return to the preamplifier. The search algorithm is reinitiated, and the entire process repeated until a satisfactory sample point is achieved without excessive signal saturation.
Another feature of the present invention is the detection of the typical daily and weekly occupancy cycles of the controlled space, and use of that information to improve the accuracy of the sensor""s occupancy decisions. This is accomplished by maintaining a clock, and dividing the seven days of the week and the 24 hours of each day into multiple time slots. Associated with each of these time slots is a stored data value that indicates the likelihood that the workspace is occupied during that particular time on that particular day of the week thus forming a histogram. This occupancy probability histogram is formed over a period of days and weeks during which the sensor records and averages the detected occupancy of the space for that particular time slot. When a marginal motion signal is received, the sensor applies a correction to it based on the probability of occupancy that has been determined for that particular time slot. If the time slot is one that is typically occupied, the occupancy decision is biased in favor of declaring occupancy and the electrical loads are turned on. Conversely, if the time slot is one that is typically not occupied, the occupancy decision is biased in favor of determining non-occupancy, and the electrical loads are kept off. The result of this algorithm is a sensor that knows when people are typically around, and energizes the electrical loads quickly for them, and knows when the space is typically vacant, and keeps the electrical loads de-energized unless an unmistakable motion signal is received.
The present invention also includes active ultrasonic continuous wave Doppler motion occupancy detection. The duty cycle of the ultrasonic transmitter waveform may be varied to achieve automatic output level adjustment. The present invention may also include PIR motion occupancy detection, acoustic sound detection, microwave detection, or any combination of ultrasonic, PIR, acoustic, and microwave detection methods.
The present invention may also include energy-conserving daylight control operation. This feature is used to turn off electrical lighting loads in an occupied area that has a sufficient amount of natural lighting or to control dimmable or multi-level lighting systems to provide only the required amount of additional (electrical) lighting.
The present invention is also able to recognize saturation of the ultrasonic receiver preamplifier due to excessive ultrasonic return signal amplitude. It is able to vary the duty cycle of the waveform applied to the ultrasonic transmitter away from 50 percent (maximum amplitude) duty cycle, and to decrease the amplitude by changing to a lower duty cycle.
The present invention also includes easy selection of operating mode and adjustment of sensitivity and timer delay. This feature allows the user to easily adjust the sensor""s mode of operation, the sensor""s sensitivity and delay timer settings for the desired operation of the sensor. A user of the present invention also has a variety of sophisticated dual-technology selection settings, including a HIGH CONFIDENCE mode and a HIGH SENSITIVITY mode.
Other features and advantages of the invention will become apparent from a consideration of the drawings and ensuing detailed description.